You can actually export to pptx and then import those files into Google Slides! I do it all the time and it translates the design over almost 100% exactly as you designed it in Pitch!

Just open Slides, and when you have a new presentation open click "File" then "Import Slides" then "Upload" and select the pptx file you saved out from Pitch. Then you can select all the pages you want to open in slides manually, and click "Import Slides". They should then open up as Google Slides!

Hope this helps and works for you.

Interesting